1. Field of the Invention
The present invention relates to a monitoring method and a monitor apparatus for monitoring, in a machine tool including a rotary shaft that is mounted with a tool or a workpiece and driven by a motor, and a rotation speed fluctuating unit that continuously fluctuates a rotation speed of the rotary shaft at an arbitrary pattern, a fluctuating condition of the rotation speed caused by the rotation speed fluctuating unit on a display section, and also relates to a machine tool equipped with the monitor apparatus.
2. Description of Related Art
When machining a workpiece with low rigidity using a machine tool or during machining that uses a tool with low rigidity, sharp vibration known as chatter vibration often occurs during cutting. Chatter vibration produces a cyclical pattern generally known as a chatter mark on the machined surface, and causes degradation of the finished surface texture and machining accuracy, Cyclic fluctuations in cutting force cause noise, which may lead to problems such as tool wear and loss.
As a method for suppressing chatter vibration, Japanese Patent Application Publication No. 49-105277 (JP 49-105277 A) describes art that fluctuates a rotation speed of a rotary shaft. Japanese Patent Application Publication No. 2000-126991 (JP 2000-126991 A) also describes an invention that enables easy operation of a control device when chatter vibration occurs by displaying a control screen for fluctuating rotation speed and allowing input per tool of a fluctuation range and fluctuation degree of the rotation speed. A previous patent application (Japanese Patent Application No. 2010-235720) filed by the applicant of the present application provides an invention that displays parameter values having an effect on regenerative chatter vibration during cutting at fluctuating rotation speeds, and enables simple setting of the parameters.
In the past, however, even if a fluctuation period is set to a minimum value within a range of operation shown to have an effect on chatter vibration as mentioned above when periodically fluctuating the rotation speed of the rotary shaft, it was not always possible to minimize chatter vibration depending on the rotation speed. Therefore, the operator could not always accurately know the optimal fluctuation period for suppressing chatter vibration, and finding the optimal parameters often took time.